I answered "do you know that boy" and it got marked as correct. But reading up on demonstrative pronouns it seems like accusative of ´that´ should be tamtego. So shouldnt my answer be wrong?
If immery was here she would give you a better answer, but basically, Polish doesn't care much about this/that distinction as long as you don't have to show the contrast between them (This dog is black and that one is white). So in most cases, both "this" and "that" are accepted here.
Whether Polish doesn't care about the difference between "this" and "that", I am going to translate "tego" as "this" and "tamtego" as "that". I just think it is easier that way since that is the correct translation for each word. Plus, we beginners don't need to be confused even more when Polish is already a very complicated language.